Recently, from the apprehension of the depletion of petroleum resources and from the viewpoint of the environmental preservation, resins made of plant-derived raw materials have been attracting attention. Among the resins made of plant-derived raw materials, polylactic acid is relatively satisfactory in heat resistance and strength, and allows mass production, and hence has been applied to various applications such as applications to packaging containers, agricultural films and housings of electric/electronic appliances.
However, polylactic acid resin is flammable, and hence when polylactic acid resin is used in applications requiring high-degree of flame retardancy such as applications to housings of electrical household appliances and OA appliances and automobile components, countermeasures for flame retardation are required. As a general method for flame retardation, it is possible to adopt a method in which a halogen-based flame retardant such as a bromine compound high in flame retardation effect is mixed in the resin. However, halogen-based flame retardants sometimes generate halogen-derived gases at the time of burning, and accordingly, it becomes necessary to cope with the exhaust gases and the work environment associated with the incineration of waste and the thermal recycle.
As flame retardation techniques involving flame retardants other than halogen-based flame retardants, metal hydroxide-based flame retardants and phosphorus-based flame retardants are added to resins.
Patent Literature 1 describes the addition of a metal hydroxide (aluminum hydroxide) and a phosphorus-containing compound(s) (triphenyl phosphate and/or a phosphinic acid salt), as a flame retardation technique for polymer compounds having biodegradability such as polylactic acid.
Patent Literature 2 describes compositions of synthetic resins (ABS resin, polyethylene terephthalate resin and epoxy resin) that contain a phosphorus compound having a phosphaphenanthrene skeleton, although no flame retardant effect of Examples is described.
Patent Literature 3 describes a phosphorus compound having a phosphaphenanthrene skeleton as a flameproofing agent for polyester fiber.
Patent Literature 4 describes a flame-retardant resin composition that contains a styrene-based resin (ABS, HIPS (impact resistant polystyrene) and a phosphorus compound having a phosphaphenanthrene skeleton.